VIDEO ALERT: Additional audio and video resources, including excerpts from an interview with Dr. Warner describing the research, are available on the Mayo Clinic News Blog.

Children exposed to two or more anesthetics before age 3 had more than double the incidence of ADHD than children who had no exposure, says David Warner, M.D., a Mayo Clinic pediatric anesthesiologist and investigator on the observational study.

When basic science studies in the medical literature began to suggest anesthesia used in surgery causes changes in the brains of young animals, Dr. Warner and a group of researchers at Mayo Clinic took note.

"Those studies piqued our interest," Dr. Warner says. "We were skeptical that the findings in animals would correlate with kids, but it appears that it does."

The study utilized results of an existing epidemiological study that looked at educational records of children born between 1976 and 1982 in Rochester, Minn., and determined those who developed some form of learning disability or ADHD.

Among 341 cases of ADHD in those younger than 19, researchers traced medical records in the Rochester Epidemiology Project, a decades-long database of all patient care in Olmsted County, Minn., looking for exposure to anesthesia and surgery before age 3.

Children who had no exposure to anesthesia and surgery had ADHD at a rate of 7.3 percent. The rate after a single exposure to anesthesia and surgery was approximately the same. For children who had two or more exposures to anesthesia and surgery, the rate of ADHD was 17.9 percent, even after researchers adjusted for other factors, including gestational age, sex, birth weight and comorbid health conditions.

The results of the study, however, do not definitively mean that anesthesia causes ADHD, Dr. Warner says.

"This is an observational study," he says. "A wide range of other factors might be responsible for the higher frequency of ADHD in children with multiple exposures. The findings certainly do suggest that further investigation into this area is warranted, and investigators at Mayo Clinic and elsewhere are actively pursuing these studies."